Field of the Invention
The present invention relates to a method for soldering a ceramic body of an electrical component into a metal housing.
In electric components with ceramic component bodies, an electrically conductive layer, which can generally be referred to as a contact lining, is applied to the ceramic body. That is the case, for instance, with temperature-dependent resistors or in microwave filters, which have a ceramic component body. That kind of contact lining may, for instance, be a copper layer or a nickel-copper layer. In the latter case, the copper is located on the outside.
Since the copper oxidizes, provisions must be made for passivating it, in order to avoid oxidation. A lead-tin layer, which preferably has a high melting point and at the same time is suitable for soldering the ceramic component body into a housing, is suitable for such passivation. A lead-tin layer of that kind applied to the surface of the ceramic body is composed of 95% lead and 5% tin, for example. That kind of lead-tin layer with a high melting point is also especially suitable because it keeps the component fixed when the customer performs low-melting-point soldering of the component to install it in a circuit.
If, as described above, the lead-tin layer is applied to the surface of the ceramic body of the component, that is done by galvanizing techniques. In other words, the ceramic body is placed in a lead-tin bath. However, that kind of process is disadvantageous for environmental reasons, and in view of wastewater treatment is substantially more cost-intensive, especially because of the heavy metal, that is lead.